Data comprising5,007 records of first lactation of Holstein cows, daughters of 930 sires, from33 herds in the state of Rio Grande do Sul, from 1984 to 1998, were used toestimate heritability coefficients and genetic trends for milk (MY) and fat(FY) yields and for fat percentage (%F). An animal model considered the geneticadditive direct and residual as random effects and milking/day number, herdand year/season of parturition, and cow age at parturition as fixed effects,linear and quadratic effects, as covariate, inn order to estimate the coefficientsof heritability and to predict the breeding values (BVs) for MY, FY and %F.The genetic trend was estimated by the regression of mean annual animal BVsin relation to animal year birth. The averages and respective standard deviationsfor MY, FY and %F were: 6,862.80 ± 1,881.21 kg/year, 228.63 ±78.01 kg/year and 3.32 ± .18 %/year, respectively. The estimated coefficientsof heritability and respective standard error for MY, FY and %F were: 0.30 ±0.008; 0.28 ± 0.004 and 0.22 ± 0.015, respectively. The estimatedgenetic correlations were: 0.85 ± 0.19 and -0.15 ± 0.17 for MYand FY and MY and F%, respectively. The genetic trend for MY was of 9.25 kg/year,0.11 kg/year for FP and -0.07%/year for %F. The values estimated for the coefficientsof heritability suggest that it is possible to increase the rates for geneticgain for MP and FP, without change on %F rate. The genetic gains for MY andFY were positive, but low, however they can be improved if breeding programsthat stimulate the dairy man to increase both traits milk quality are implemented.
